If you have not raised many litters out of this line of dogs I would say wait and give them a little time. But keep note on all the pups the good and the bad. I have been around my dogs long enough to know them very well. I start culling the minute they are born. Good luck with them.
X2, Culling is a progression, as the pups grow, they are on a point system which means that all pups in the litter are getting tested in all the things they do or don't do. If you are a breeder you should know how the pups develop and what is a cull. I have culled pups at 4 months that turned out great. When I cull young pups it only means that they are not good enough for me at that age but it doen't mean they will not hunt. I want to see a lot of potential at a young age. As the pup gets older he/she should be progressing or will get culled. The older the cull from my yard the better it is because it had to be pretty good to last that long. Serious breeders do it that way.
The way I see it if you pick early starting dogs then those dogs will produce early starting dogs and those percentages will keep increasing in your favor.
Also, I do like outgoing pups but the very best sometimes are laid back easy going, not hyper in any way but when the tailgate drops these dogs will put on a hogdog clinic...
I am always on the lookout for these types...
Another thing to consider is the strain and breed of dog as to when you cull.
Life is too short to finally cull at 1.5 yrs. or worse at 2 yrs. If the dog finally makes it at 2 yrs. of age I wouldn't breed it and it would be on the replacement list.